1. Field of the Invention
The present invention relates to a material for use in microwave band devices which are used by the general people and in industrial electronic apparatuses. Particularly, the present invention relates to a magnetic ceramic composition for use in microwave devices, a magnetic ceramics for use in microwave devices and a preparation method therefor, in which the saturation magnetization can be easily controlled, and a low ferri-magnetic resonance half line width and an acceptable curie temperature are ensured.
2. Description of the Prior Art
Recently, in accordance with the universal use of the communication means such as car phones, portable phones, cordless phones, and satellite broadcasting receiver, there have been much progresses in the microwave circuits and integrated circuits. Accordingly, the trend is that magnetic ceramics are widely used in microwave devices such as isolators, circulators, S/N enhancers and the like.
Such magnetic ceramics for microwave devices are used mostly in isolators and circulators. The conventional typical magnetic ceramics are YIG (Y.sub.3 Fe.sub.5 O.sub.12), Ni-Zn ferrites, Mn-Mg ferrites and Li ferrites.
Meanwhile, if the magnetic ceramics for the microwave devices is to be applied to the microwave band components such as isolators and circulators, a proper saturation magnetization in which adjustments should be possible in a range of 100-1,800 G should be ensured. Further, in the microwave band, the ferri-magnetic resonance half line width should be as low as 60 Oe, and the temperature coefficient for the saturation magnetization should be as low as 0.2%/.degree.C. If the temperature coefficient for the saturation magnetization is high, a temperature stability cannot be obtained, and if the ferri-magnetic resonance half line width is high, the loss characteristics in the microwave band is aggravated.
However, among the conventional magnetic ceramics for the microwave devices, the YIG series show a proper saturation magnetization, a low ferri-magnetic resonance half line width, but a relatively high temperature coefficient of 0.3-0.4%/.degree.C. for the magnetic saturation.
Meanwhile, in the case of the Ni-Zn ferrites and the Mn-Mg ferrites, the saturation magnetization is high, and the temperature coefficient is relatively low, but the ferri-magnetic resonance half line width is as high as 160 Oe.
Meanwhile, in the case of the Li ferrites, the saturation magnetization is proper, and the temperature coefficient is low, but the ferri-magnetic resonance half line width is as high as 300 Oe.
Therefore, the above described conventional magnetic ceramics for the microwave devices have practical problems in applying to the microwave band components. Further, during the preparation of the magnetic ceramics, there are used expensive raw materials such as yttrium oxide, iron oxide and the like, with the result that the economy is aggravated.